Low pressure bleed architecture

ABSTRACT

A bleed air conditioning system within an aircraft including a low-pressure bleed air line and a high-pressure bleed air line. The system includes an air-to-air heat exchanger and an un-cooled bleed air line to connect the air-to-air heat exchanger to the low-pressure bleed air line and the high-pressure bleed air line. The un-cooled bleed air line carries a flow of un-cooled bleed air from at least one of the low-pressure bleed air line and the high-pressure bleed air line to the air-to-air heat exchanger. The system also includes a cooled bleed air line connected to the air-to-air heat exchanger for carrying cooled bleed air from the air-to-air heat exchanger and a low-pressure bypass line connecting the low-pressure bleed air line to the cooled bleed air line, bypassing un-cooled bleed air from the low-pressure line around the air-to-air heat exchanger to the cooled bleed air line.

BACKGROUND

The present invention relates to aircraft environmental control systems.In particular, the invention relates to bleed air systems for supplyingcompressed air to an aircraft environmental control system.

Aircraft environmental control systems maintain aircraft cabin airpressures and temperatures within a target range for the safety andcomfort of aircraft passengers. This is done through the use ofcompressed air taken from two compressor stages (bleed air) of theturbine engines propelling the aircraft. Each of the two air pressuresavailable from the compressor, low pressure (LP) and high pressure (HP),are directed to the environmental control system (ECS) through pressurelines or plenums. A pneumatic valve controller operates a series ofpneumatically operated bleed valves in response to electronic controlsignals from the ECS (or from a dedicated ECS bleed valve controller) tocontrol the relative flows of LP and HP compressed air flowing to theECS. The LP and HP bleed air as taken from the compressor is at a veryelevated temperature due to the natural increase in the temperature of agas as it is compressed. Thus, before the bleed air flows to the ECS,where it is cooled to a desired cabin temperature, it is “pre-cooled” byflowing through an air-to-air heat exchanger known as a “pre-cooler.”Cool fan air from the bypass region of the engine also flows through thepre-cooler to cool the bleed air. Air pressure in the bleed air lines ismeasured by at least one pressure sensor which provides this informationto the ECS. Similarly, air temperature in the bleed air lines ismeasured by at least one temperature sensor which provides thisinformation to ECS. The ECS uses the air pressure and temperatureinformation along with other information from around the aircraft todirect the pneumatic valve controller to provide bleed air at a desiredpressure to the environmental control system. The ECS also directs a fanair valve to adjust the flow of fan air to the pre-cooler to providebleed air to the ECS at a desired temperature.

SUMMARY

The present invention concerns a bleed air conditioning system within anaircraft including a low-pressure bleed air line carrying bleed air at afirst pressure from a compressor and a high-pressure bleed air linecarrying bleed air at a second pressure from the compressor, in whichthe second pressure is higher than the first pressure. The system alsoincludes an air-to-air heat exchanger cooled by a cooling air flow andan un-cooled bleed air line to connect the air-to-air heat exchanger tothe low-pressure bleed air line and the high-pressure bleed air line.The un-cooled bleed air line carries a flow of un-cooled bleed air fromat least one of the low-pressure bleed air line and the high-pressurebleed air line to the air-to-air heat exchanger. The system alsoincludes a cooled bleed air line connected to the air-to-air heatexchanger for carrying cooled bleed air from the air-to-air heatexchanger and a low-pressure bypass line connecting the low-pressurebleed air line to the cooled bleed air line, bypassing un-cooled bleedair from the low-pressure line around the air-to-air heat exchanger tothe cooled bleed air line.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side schematic view of a bypass turbine engine and pylonincorporating a low pressure bleed system of the present invention.

FIG. 2 is a more detailed side schematic view of a portion of FIG. 1illustrating an embodiment of a low pressure bleed system of the presentinvention.

FIG. 3 is a more detailed side schematic view of a portion of FIG. 1illustrating another embodiment of a low pressure bleed system of thepresent invention.

DETAILED DESCRIPTION

Conventional bleed systems direct LP bleed air through a pre-cooler tothe ECS, until a higher pressure is required by the ECS. Then HP bleedair is directed through the pre-cooler to the ECS. Although HP bleed airis much hotter than LP bleed air, both LP and HP bleed air are too hotfor use by the ECS and must be pre-cooled. Pre-cooling decreases thepressure of the bleed air flowing to the ECS. Under normal flightconditions, the LP air is generally sufficient for all ECS requirements.However, under low throttle settings, for example, aircraft descent,when the engines are idling, the LP bleed air pressure is notsufficient, once pre-cooled, to meet the demands of the ECS. Under theseconditions, much hotter HP bleed air is used. The flow of HP bleed airunder low throttle settings represents the greatest cooling loadrequirement for the pre-cooler and determines the size of thepre-cooler.

In the present invention the LP bleed air line splits into two parallelLP bleed air lines, one joining the HP bleed air line and directed tothe pre-cooler and another that bypasses the pre-cooler, joining thebleed air line beyond the pre-cooler. By splitting the flow such that aportion bypasses the pre-cooler, the pressure drop in the LP bleed airassociated with the pre-cooler is reduced. Thus, the bleed air pressureavailable to the ECS on LP bleed air is higher for a given throttlesetting than it would be without the LP bypass. As a result, HP bleedair is not required until a comparatively lower throttle setting thanwithout the LP bypass. At the comparatively lower throttle setting, thetemperature of the HP bleed air is also comparatively lower such thatthe pre-cooler size can be smaller and the pre-cooler lighter. A smallerpre-cooler saves space within the aircraft and a lighter pre-coolerreduces fuel consumption. In addition, drawing high temperature HP bleedair from the engine results in a large energy penalty. By delaying theshift to HP bleed air until the engine is at a lower throttle setting,the HP bleed air is withdrawn at a lower temperature and for a shorterperiod of time, reducing the energy penalty.

FIG. 1 is a side schematic view of a bypass turbine engine and pylonincorporating a low pressure bleed system of the present invention. FIG.1 shows aircraft propulsion system 10 attached to aircraft wing 12 andincludes bypass turbine engine 14 and pylon 16. Bypass turbine engine 14includes fan 18, turbine engine shaft 20, compressor 22, combustor 23,turbine 24, exhaust nozzle 26, LP bleed air line 28, HP bleed air line30, and engine mount beam 31. Pylon 16 includes fan air plenum 32, bleedair conditioning system 34, and cooled bleed air line 36.

Pylon 16 connects bypass turbine engine 14 at engine mount beam 31 towing 12. Compressor 22 connects fan 18 and combustor 23. Combustor 23connects compressor 22 and turbine 24. Exhaust nozzle 26 is attached toturbine 24. Turbine engine shaft 20 is connected to fan 18, compressor22, and turbine 24. LP bleed air line 28 and HP bleed air line 30 areattached to stages of compressor 22 providing air of low pressure andhigh pressure, respectively. LP bleed air line 28 and HP bleed air line30 are also attached to bleed air conditioning system 34 in pylon 16.Fan air plenum 32 extends from bypass turbine engine 14, through enginemount beam 31, bleed air conditioning system 34, and out pylon 16.Cooled bleed air line 36 extends from bleed air conditioning system 34through pylon 16 to wing 12 and on to the environmental control system(not shown).

In operation, air is compressed in stages by compressor 22 and ignitedwith fuel in combustor 23 to produce rapidly expanding gasses that driverotation in turbine 24. The expanding gasses exit exhaust nozzle 26providing a portion of the engine thrust. Turbine 24 rotates attachedturbine engine shaft, providing power for the compression of air incompressor 22 and for the rotation of fan 18. Fan 18 rotates to providea flow of fan air (F) through bypass turbine engine 14. The flow of fanair exiting bypass turbine engine 14 near nozzle 26 provides the balanceof the engine thrust. A portion of the fan air (fan bleed air) flowsinto fan air plenum 32 for use by bleed air conditioning system 34. LPbleed air line 28 and HP bleed air line 30 direct air from the lowpressure and high pressure stages, respectively, of compressor 22 tobleed air conditioning system 34. Bleed air conditioning system 34 useslow pressure bleed air provided by LP bleed air line 28, high pressurebleed air provided by HP bleed air line 30, and fan bleed air providedby fan air plenum 32 to deliver cooled bleed air to the ECS throughcooled bleed air line 36 at a temperature and pressure required by theECS.

FIG. 2 is a more detailed side schematic view of a portion of FIG. 1illustrating an embodiment of a low pressure bleed system of the presentinvention. FIG. 2 shows bleed air conditioning system 34 including LPbleed air line 28, HP bleed air line 30, fan air plenum 32, cooled bleedair line 36, pre-cooler 38, un-cooled bleed air line 40, and LP bypassline 42. LP bleed air line 28 comprises first LP check valve 44 andsecond LP check valve 46. HP bleed air line 30 comprises HP bleed valve48. Fan air plenum 32 comprises fan bleed valve 50. LP bypass line 42comprises LP bypass orifice 52. Cooled bleed air line 36 comprises bleedair pressure regulator and shut-off valve 54, pressure sensor 56, andtemperature sensor 58.

LP bleed air line 28 and HP bleed air line 30 connect to un-cooled bleedair line 40. First check valve 44 and second check valve 46 are orientedin LP bleed air line 28 to prevent bleed air from flowing towardcompressor 22 of FIG. 1. HP bleed valve 48 controls the flow ofhigh-pressure bleed air from compressor 22 of FIG. 1. Pre-cooler 38connects un-cooled bleed air line 40 to cooled bleed air line 36.Pre-cooler 38 is an air-to-air heat exchanger connected to fan airplenum 32 such that there is efficient heat transfer between the bleedair flow through pre-cooler 38 and the fan bleed air flow (F) throughpre-cooler 38, without mixing of the bleed air flow and the fan bleedair flow. Fan bleed valve 50 controls the flow of fan bleed air intopre-cooler 38. LP bypass line 42 connects LP bleed air line 28 to cooledbleed air line 36, bypassing LP bleed air from LP bleed air line 28around pre-cooler 38. LP bypass line 42 connects to LP bleed air line 28at a point between first check valve 44 and second check valve 46. LPbypass orifice 52 produces a pressure drop in the flow through LP bypassline 42. Pressure regulator and shut-off valve 54 is downstream of thepoint at which LP bypass line 42 connects to cooled bleed air line 36.Pressure sensor 56 and temperature sensor 58 are downstream frompressure regulator and shut-off valve 54.

In operation, bleed air conditioning system 34 supplies cooled bleed airat a desired pressure and temperature in response to electronic controlsignals from the ECS (not shown) directed to HP bleed valve 48, fanbleed valve 50, and pressure regulator and shut-off valve 54. Pressuresensor 56 and temperature sensor 58 provide measurements to the ECS.Under nominal throttle settings, for example, during sustained flight ortakeoff, LP bleed air pressure is sufficient for ECS requirements. LPbleed air flows from LP bleed air line 28 through second check valve 46.Beyond second check valve 46, the LP bleed air flow splits into a firstportion of LP bleed air and a second portion of LP bleed air where LPbypass line 42 connects to LP bleed air line 28.

The first portion of LP bleed air continues in LP bleed air line 28,through first check valve 44, into un-cooled bleed air line 40, and intopre-cooler 38. The first portion of LP bleed air is cooled as it flowsthrough pre-cooler 38 by heat transfer to fan bleed air also flowingthrough pre-cooler 38. Fan bleed valve 50 is adjusted by the ECS toprovide the fan bleed air flow necessary to achieve cooling required bythe ECS. The heat transfer is by conduction through a heat exchangesurface of relatively large area, and by convection to and from the heatexchange surface by the first portion of LP bleed air flow and the fanbleed air flow, respectively. At no point in pre-cooler 38 does flow ofthe first portion of LP bleed air and the flow of fan bleed airintermix. The cooled first portion of LP bleed air flows from pre-cooler38 into cooled bleed air line 36. Simultaneously, the second portionflows through LP bypass line 42, through LP bypass orifice 52, to cooledbleed air line 36. At cooled bleed air line 36, the cooled first portionof LP bleed air and the un-cooled second portion of LP bleed airrecombine. To achieve the desired temperature in cooled bleed air line36, the first portion of LP bleed air must be overcooled in pre-cooler38 so that when combined with the un-cooled second portion of LP bleedair, the bleed air temperature in cooled bleed air line 36 is thetemperature required by the ECS. Because pre-cooler 38 is sized, asnoted above, to cool HP bleed air under low throttle settings,overcooling the first portion of LP bleed air is well within thecapability of pre-cooler 38. Finally, pressure regulator and shut-offvalve 54 adjusts the cooled bleed air flow to achieve the pressurerequired by the ECS.

At sufficiently low throttle settings, LP bleed air pressure is notsufficient for ECS requirements. Under these conditions, HP bleed valve42 opens and HP bleed air flows from HP bleed air line 30 in toun-cooled bleed air line 40. The HP bleed air causes first LP checkvalve 44 to close, preventing any flow between LP bleed air line 28 andpre-cooler 38 and preventing any flow of HP bleed air back intocompressor 22 of FIG. 1. The HP bleed air flows into un-cooled bleed airline 40, and into pre-cooler 38. The HP bleed air is cooled as it flowsthrough pre-cooler 38 as describe above for the first portion of LPbleed air. However, because the HP bleed air is much hotter than the LPbleed air, fan bleed valve 50 is directed open further to increase theflow of fan bleed air. This represents the largest cooling load forpre-cooler 38 and determines the capacity of pre-cooler 38. The cooledHP bleed air flows from pre-cooler 38 into cooled bleed air line 36. Thecooled HP bleed air increases the pressure in LP bypass line 42, causingsecond LP check valve 46 to close, again preventing any flow of HP bleedair back into compressor 22. Pressure regulator and shut-off valve 54adjusts the cooled bleed air flow to achieve the pressure required bythe ECS.

Pre-cooling decreases the pressure of the cooled LP bleed air relativeto the un-cooled LP bleed air due to the pressure restriction caused bythe flow of bleed air through pre-cooler 38. LP bypass line 42 must besized to create some pressure drop along its length to balance the flowof the first portion of LP bleed air through pre-cooler 38 and the flowof the second portion of LP bleed air through LP bypass line 42. If LPbypass line 42 presents too little restriction to flow, the cooled firstportion of LP bleed air becomes too small, when combined with muchlarger un-cooled second portion of LP bleed air, to provide the requiredtemperature in cooled bleed air line 36 under a condition of maximum LPbleed temperature. Alternatively, as shown in FIG. 2, LP bypass orifice52 is sized to produce a pressure drop in the flow through LP bypassline 42 sufficient to provide a balanced (but not necessarily equal)flow between the first portion of LP bleed air and the second portion ofLP bleed air. Although this places a flow restriction comparable to thatof pre-cooler 38 in LP bypass line 42, the pressure drop from LP bleedair line 28 to cooled bleed air line 36 is reduced because the LP bleedair flows through two channels, each carrying a lower flow rate thanwould be required to go through pre-cooler 38 in the absence of LPbypass line 42.

FIG. 3 is a more detailed side schematic view of a portion of FIG. 1illustrating another embodiment of a low pressure bleed system of thepresent invention. Bleed air conditioning system 134 shown in FIG. 3 isidentical to bleed air conditioning system 34 shown in FIG. 2, exceptthat second LP check valve 46 is omitted from LP bleed air line 28 andan identical second LP check valve 146 is included in LP bypass line 42.Operation is also the same, except that the second portion of LP bleedair flows through LP bypass line 42, through LP bypass orifice 52, andthrough second LP check valve 146 before reaching cooled bleed air line36. The biggest difference in operation between the embodiments of FIG.3 and FIG. 2 is when HP bleed air flow is required. After the cooled HPbleed air flows from pre-cooler 38 into cooled bleed air line 36,instead of increasing the pressure in LP bypass line 42, second checkvalve 146 closes, preventing an increase of pressure in LP bypass line42, as well as preventing any flow of HP bleed air back into compressor22.

In all embodiments of the present invention, by splitting the LP bleedair line into two parallel LP bleed air lines, one joining the HP bleedair line and directed to the pre-cooler, and the other bypassing thepre-cooler and joining the bleed air line beyond the pre-cooler, thepressure drop in the LP bleed air associated with the pre-cooler isreduced. Thus, the bleed air pressure available to the ECS from LP bleedair is higher for a given throttle setting than it would be without theLP bypass. As a result, HP bleed air is not required until acomparatively lower throttle setting than without the LP bypass. At thecomparatively lower throttle setting, the temperature of the HP bleedair is also comparatively lower such that the pre-cooler size can besmaller and the pre-cooler lighter. A smaller pre-cooler saves space ata critical location within the aircraft (e.g. pylon, nacelle, etc.) anda lighter pre-cooler reduces fuel consumption. In addition, drawing hightemperature HP bleed air from the engine results in a large energypenalty. By delaying the shift to HP bleed air until the engine is at alower throttle setting, the HP bleed air is withdrawn at a lowertemperature and for a shorter period of time, reducing the energypenalty.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

1. A bleed air conditioning system within an aircraft, the systemcomprising: a low-pressure bleed air line for carrying bleed air at afirst pressure from a compressor; a high-pressure bleed air line forcarrying bleed air at a second pressure from the compressor, wherein thesecond pressure is higher than the first pressure; an air-to-air heatexchanger cooled by a cooling air flow; an un-cooled bleed air lineconnecting the low-pressure bleed air line and the high-pressure bleedair line to the air-to-air heat exchanger for carrying a flow ofun-cooled bleed air from at least one of the low-pressure bleed air lineand the high-pressure bleed air line to the air-to-air heat exchanger; acooled bleed air line connected to the air-to-air heat exchanger forcarrying cooled bleed air from the air-to-air heat exchanger; and alow-pressure bypass line connecting the low-pressure bleed air line tothe cooled bleed air line for bypassing un-cooled bleed air from thelow-pressure line around the air-to-air heat exchanger to the cooledbleed air line.
 2. The bleed air conditioning system of claim 1,wherein: the low-pressure bleed air line comprises a first check valveand a second check valve, wherein the first check valve is upstream fromthe second check valve and wherein both check valves are oriented toprevent bleed air flow in the direction of the compressor; thehigh-pressure bleed air line comprises a bleed valve to control the flowof bleed air from the compressor; and the low-pressure bypass lineconnects to the low-pressure bleed air line at a point between the firstcheck valve and the second check valve.
 3. The bleed air conditioningsystem of claim 1, wherein: the low-pressure bleed air line comprises afirst check valve, wherein the first check valve is oriented to preventbleed air flow in the direction of the compressor; the low-pressurebypass line comprises a second check valve and connects to thelow-pressure bleed air line at a point upstream of the first checkvalve; and the high-pressure bleed air line comprises a bleed valve tocontrol the flow of bleed air from the compressor.
 4. The bleed airconditioning system of claim 1, wherein the low-pressure bypass linecomprises an orifice for balancing the flow of bleed air through thelow-pressure bypass line with the flow of bleed air at the firstpressure through the air-to-air heat exchanger.
 5. The bleed airconditioning system of claim 1, wherein the cooled bleed air linecomprises a pressure regulator and a shut-off valve, the pressureregulator and shut-off valve located downstream of the point ofconnection between the low-pressure bypass line and the cooled bleed airline.
 6. The bleed air conditioning system of claim 5, wherein thecooled bleed air line further comprises at least one of a pressuresensor and a temperature sensor, the pressure sensor and the temperaturesensor located downstream of the pressure regulator and the shut-offvalve.
 7. The bleed air conditioning system of claim 1, furthercomprising a fan air plenum connected to the air-to-air heat exchangerfor providing the cooling air flow, wherein the cooling air flowcomprises fan bleed air.
 8. The bleed air conditioning system of claim7, wherein the fan air plenum comprises a fan bleed valve to control theflow of fan bleed air to the air-to-air heat exchanger.
 9. The bleed airconditioning system of claim 1, wherein the cooled bleed air line isconnected to an environmental control system for providing cooled bleedair to the environmental control system.
 10. A method for decreasing athrottle setting at which a gas turbine-powered aircraft must switchfrom low-pressure bleed air to a high-pressure bleed air, the methodcomprising: flowing low-pressure bleed air from a compressor at a firstpressure; directing a first portion of the low-pressure bleed air to anair-to-air heat exchanger; cooling the first portion of the low-pressurebleed air in the air-to-air heat exchanger; flowing the first portion ofthe low-pressure bleed air from the air-to air heat exchanger into acooled bleed air line; directing a second portion of the low-pressurebleed air to a low-pressure bypass line; and flowing the second portionof the low-pressure bleed air from the low-pressure bypass line into thecooled bleed air line.
 11. The method of claim 10, further comprising:flowing high-pressure bleed air from a compressor at a second pressure,wherein the second pressure is greater than the first pressure;preventing the flow of the first portion of low-pressure bleed air tothe air-to-air heat exchanger by flowing the high-pressure bleed air;preventing the flow of the second portion of low-pressure bleed air tothe cooled bleed air line by flowing the high-pressure bleed air;directing the high-pressure bleed air to the air-to-air heat exchanger;cooling the high-pressure bleed air in the air-to-air heat exchanger;and flowing the high-pressure bleed air from the air-to air heatexchanger into a cooled bleed air line.
 12. The method of claim 11,wherein preventing the flow of the first portion of low-pressure bleedair to the air-to-air heat exchanger by flowing the high-pressure bleedair and preventing the flow of the second portion of low-pressure bleedair to the cooled bleed air line by flowing the high-pressure bleed airis performed by check valves.
 13. The method of claim 10, furthercomprising: balancing the flow of the second portion of low-pressurebleed air through the low-pressure bypass line with the flow of thefirst portion of low-pressure bleed air through the air-to-air heatexchanger.